This invention relates to systems for adding or removing heat from a confined space in order to control the temperature in that space. In particular, this invention relates to hydronic systems which employ water as the heat exchange medium for adding or removing heat from a confined space.
Hydronic systems may employ different approaches as to how to deliver water to spaces that are to be heated or cooled. For instance, hydronic systems may use a first conduit to deliver heated water and a second conduit to deliver cooled water to one or more heat exchangers servicing the spaces to be heated or cooled. These systems will also use separate return conduits to circulate the water back to the heating and cooling sources which heat or cool the water before it is again delivered to the one or more heat exchangers. The above described hydronic systems are often referred to as “four pipe” hydronic systems because there are two delivery conduits or pipes which deliver the water to the one or more heat exchangers and two return conduits or pipes which circulate water back to the heating and cooling sources.
Another type of hydronic system uses a single conduit to deliver either heated or cooled water from the heating or cooling sources to the one or more heat exchangers in the spaces to be heated or cooled. This type of hydronic system will also use a single return conduit to circulate the water from the one or more heat exchangers back to the heating and cooling sources. This latter type of hydronic system is typically referred to as a “two-pipe” system because the one or more heat exchangers have one common supply conduit or pipe and one common return conduit or pipe.
The above-described two-pipe hydronic system provides a flow of water to the various heat exchangers at an appreciably lower cost in terms of piping versus the “four-pipe” hydronic system. However the two pipe system cannot easily change from circulating heated water to circulating cooled water to the heat exchangers. In this regard, the cooling source which could be a chiller does not perform well when it is receiving substantially warm water in the return line as a result of the two pipe system having previously been in a heating mode. The same is true for a boiler that is receiving substantially cooler water than it normally is deigned to operate with.
The inability to changeover or switch the two-pipe hydronic system between heating and cooling or vice versa has previously led to switching the system to either heating or cooling, depending on the season of the year. For instance, changeovers would be implemented on particular calendar dates indicating normal change of seasonal weather conditions. On the other hand, a changeover might be implemented depending on a separately sensed outdoor air temperature indicating whether the two-pipe hydronic system should be in either heating or cooling for the day. The above described changeover controls do not allow a hydronic system to respond to heating or cooling demands that may change throughout the day. The above described systems moreover do not respond to different demands for cooling or heating throughout a building on a given day.